This type of phase varying apparatus is disclosed in, for example, Japanese Patent Early Publication H4-272411. This apparatus has a movable plate 3 mounted between a drive member (sprocket) 1, to which driving power of a crank shaft of the engine is transmitted, and a camshaft 2 of a valve mechanism, the apparatus configured to vary the relative phase of the drive member 1 and camshaft 2 by axially moving the movable plate 3, as shown in FIG. 11. That is, by means an electromagnetic brake means 4 that is pinned not to rotate, a retarding or braking force is acted on a rotational drum 5 rotatably supported by the camshaft 2 to thereby delaying the rotational drum 5 relative to the drive member 1, which in turn causes an axial movement of the movable plate 3 to rotate the camshaft 2 relative to the drive member 1, resulting in a change in phase between the drive member 1 and camshaft 2. The apparatus is installed inside the engine room of the engine so that it operas in engine oil atmosphere.
The electromagnetic brake means 4 is constituted an annular housing 4b having a U-shaped cross section for housing an electromagnetic coil 4a, a root member 4c for closing an opening of the housing 4b, and a friction member 4d bonded to the root member 4c. This apparatus has a drawback in that when the sliding surfaces of the friction member 4d of the housing 4b and the rotational drum 5 are heated to a high temperature due to friction between them, the surface of the friction member 4d which is generally made of a porous material is clogged with deposits of antioxidant, friction modifier, reactants of additives such as detergent dispersant, and insoluble compositions dispersed in the engine oil, thereby losing frictional torque generated between the friction member 4d and the rotational drum 5.
Hence, in order to cool and suppress heating of the sliding surfaces of the friction member 4d of the housing 4b and the rotational drum 5, the apparatus is provided with an oil passage 6a, a cross hole 6b, a cavity 6c, and a cross hole 6d in the camshaft 2, an annular cavity 6e formed between the camshaft 2 and the housing 4b, and a notch 6f formed on the leading edge of the peripheral wall of the housing 4b to supply the engine oil to the sliding surfaces of the friction member 4d and the rotational drum 5.
Thus, the conventional electromagnetic-brake cooling structure is passably satisfactory in cooling the sliding surface of the friction member.
However, in order to suppress the heating of the sliding surface of the friction member at even higher temperatures, a further innovated efficient cooling measure is necessary.
Thus, the inventor of the present invention has fully examined conventional cooling structures in which the engine oil supplied between the friction member 4d and the rotational drum 5 is merely scattered outwardly by a centrifugal force, and has reached a concept of new cooling structure, in which oil lead-out grooves (or notches) are formed in the leading edge of the outer peripheral wall of the housing 4b to outwardly drain the oil staying between the sliding surfaces of the friction member 4d and the rotational drum 5, so that the amount of oil lead to the sliding sections of the friction member 4d and the rotational drum 5 is increased and circulation of the engine oil is enhanced to thereby cool the sliding surfaces. In fact, it is found in numerous experiments that this inventive structure is effective.
In view of the prior art problems and the inventor's finding as mentioned above, it is an object of the invention to provide a cooling structure effective in suppressing heating of the sliding surfaces of the friction member and the rotational drum of an electromagnetic-brake of a phase-varying apparatus for use with an automobile engine, the cooling structure adapted to enhance the circulation of engine oil to cool the sliding surfaces.